Atmosphere models

The conversion of the theoretical tracks and isochrones of the present compilation to observational colour-magnitude (c-m) diagrams has been performed using the stellar spectral library of Lejeune et al. (1997, 1998) that provides empirically and semi-empirically colour-calibrated model atmosphere spectra for a large range of fundamental stellar parameters, (2000 K to 50,000 K), (-1.0 to 5.5), and (5.0 to +1.0).

For the present calculations, we use the most recent version of this library (Westera et al. 1999), Ba Se L-2.2, in which (1) all the model spectra of stars with K are now calibrated upon empirical colours from the versus relation of Flower (1996), and (2) the calibration procedure for the cool giant model spectra has been extended to the parameter ranges 2500 K 6000 K and -1.0 3.5 , with in particular the effect to provide redder model colours for giants, in better agreement with observed red giant branches of metal-poor globular clusters (see Lejeune & Buser 1999).